1. Field of the Invention
The instant invention relates to compositions for insulating electrical machinery and more particularly to aqueous unsaturated polyester emulsion blends that are thermally or radiation cured.
2. Discussion of Background Information
Organic resin compositions are used as coatings for the mechanical, electrical and environmental-resistance they impart to electromagnetic devices. The coatings provide a mechanical strength, electrical insulation, and environmental protection for improved long-term durability of the devices, as well as increasing the quality of the final product.
Suitable chemistries for the coating resin include, but are not limited to, unsaturated polyesters, epoxies, urethanes, waterborne polyesters, epoxy emulsions, silicones, organic solvent borne alkyds, acrylated and methacrylated urethanes, acrylated and methacrylated epoxies, acrylated and methacrylated polyols, and acrylated and methacrylated vegetable oils.
Many of the chemistries including unsaturated polyester resins (UPE) contain volatile reactive monomers such as styrene, vinyl toluene (VT), acrylates, and diallylphthalate (DAP). Each of these monomers have significant drawbacks in use as electrical insulating varnishes. Styrene and VT have high vapour pressure and low flashpoints leading to environmental and safety concerns. Acrylates carry an unpleasant odor in addition to being expensive and having poor viscosity reduction of the unsaturated polyester resin. DAP also requires very high concentrations to achieve suitable viscosity for impregnation of the electromechanical device such as a rotor or stator in an electric motor. Even with a low vapor pressure monomer such as DAP, volatile organic content (VOC) emissions of 1.3 lbs/gallon are observed. UPE resins also have stability issues with only 6 months of shelf life before increases in viscosity are observed.
Waterborne resins typically contain a co-solvent that adds to the VOC emissions of the system. Waterborne resins are also cured with melamine resins which potentially emits hazardous air pollutants (HAP) such as formaldehyde. Aqueous epoxy emulsions are VOC and HAP free but are very expensive compared to the other chemistries. What is desired is an aqueous coating that is cost effective like an unsaturated polyester but without the VOC and HAPS issues present with current technologies.
Documents that disclose emulsions of unsaturated polyester resin are for example US 2012/0328795 A1, U.S. Pat. Nos. 5,369,139, 5,786,420, 6,080,807, 6,380,281 B1, 7,396,882 B2, US 2009/0208864 A1, US 2010/0316947 A1. The disclosures of all of these documents and the remaining documents mentioned in the instant specification are expressly incorporated by reference herein in their entireties.
Compositions with low levels of monomer or no monomer usually are very high viscosity materials (7000 cps/7000 mPas) that are not suitable for impregnation of motors/stators.
In view of the foregoing, it would be advantageous to be able to provide compositions, especially for electrical insulation, that offer a wide variety of properties all in conjunction. Specifically, they should have very good storage stability/shelf-life of one year or more, be very cost effective similar to unsaturated polyesters both in preparation and handling, be aqueous compositions showing no VOC and/or HAPS issues, have low enough viscosities without reactive diluents that allow for good application, especially when impregnating electromechanical devices, and at the same time should have chemical/mechanical properties that equal or surpass those of previous compositions.
Other objects are apparent to those skilled in the art from the following discussion of the present invention.